First report of lineage EU23 causing potato and tomato late blight in South Africa.

In South Africa, potato () late blight epidemics from 1996 to 2007 were caused by clonal lineage US-1 (McLeod et al. 2001; Pule et al. 2013).

Effect of Sampling Time, Quantification Method, and Tree Sample Pooling on Root Quantities in South African Avocado Orchards.

is a destructive soilborne pathogen causing Phytophthora root rot on avocados worldwide. Little is known about the effect of root sampling time, root quantification method (quantitative real-time PCR [qPCR] versus baiting), and tree sample pooling strategies on the quantification of the pathogen in roots in avocado orchard trees. This was investigated in six avocado orchards in two climatically different production regions (Mooketsi and Letaba) in the Limpopo Province, South Africa, over a 2-year period.

First report of causing dieback of honeybush in the Western Cape, South Africa.

Honeybush ( spp.) is an indigenous, leguminous member of the Cape fynbos biome growing in the coastal winter rainfall districts of the Western and Eastern Cape Provinces of South Africa (Joubert et al. 2011).

Spatial and Temporal Genetic Analyses of in Two Lemon Orchards in South Africa Reveal a Role of Asexual Reproduction Within Sexually Reproducing Populations.

Citrus black spot (CBS), caused by , is a disease that affects citrus worldwide. In different regions of the world where both mating types occur, reports differ as to whether asexually produced pycnidiospores play an important role in the epidemiology of CBS and fruit infections. Therefore, we investigated the potential role of pycnidiospores in two lemon orchards in South Africa by using microsatellite-based analysis of fruit populations over time (two seasons) and space (distance).

Phosphonic acid: a long-standing and versatile crop protectant.

Phosphonic acid-based fungicides, also referred to as phosphonates, have been used extensively as crop protectants in horticulture since the late 1970s, and more recently in native ecosystems and forestry. Discovering that phosphonates are effective against foliar and soilborne oomycete diseases, such as those caused by species of Phytophthora, Pythium and Plasmopara, was a significant breakthrough, especially for soilborne pathogens that are notoriously difficult to manage. Phosphonates have played an important role in protection of forests and sensitive natural ecosystems, under threat from these pathogens.

Novel approaches and methods for quantifying Phytophthora cinnamomi in avocado tree roots.

Phytophthora cinnamomi Rands is a devastating root rot pathogen of avocado. Robust and sensitive root quantification methods are required for determining seasonal P. cinnamomi root colonization patterns and evaluating management strategies.

Two clonal lineages of Phytophthora citrophthora from citrus in South Africa represent a single phylogenetic species.

Phytophthora citrophthora from citrus in eastern Corsica and Spain consists of distinct clonal lineages. In South Africa the extent of genetic variation among citrus-associated P. citrophthora isolates is unknown.

Phytophthora niederhauserii sp. nov., a polyphagous species associated with ornamentals, fruit trees and native plants in 13 countries.

A non-papillate, heterothallic Phytophthora species first isolated in 2001 and subsequently from symptomatic roots, crowns and stems of 33 plant species in 25 unrelated botanical families from 13 countries is formally described here as a new species. Symptoms on various hosts included crown and stem rot, chlorosis, wilting, leaf blight, cankers and gumming. This species was isolated from Australia, Hungary, Israel, Italy, Japan, the Netherlands, Norway, South Africa, Spain, Taiwan, Turkey, the United Kingdom and United States in association with shrubs and herbaceous ornamentals grown mainly in greenhouses.

Pythium spp. Associated with Rooibos Seedlings, and Their Pathogenicity Toward Rooibos, Lupin, and Oat.

Rooibos (Aspalathus linearis) is an important indigenous crop in South Africa. Oomycetes are a common problem in rooibos nurseries, causing serious losses, but limited information is available on the species involved. Molecular and morphological analyses of 117 oomycete isolates from 19 rooibos nurseries and 33 isolates from 11 native rooibos sites revealed the presence of several Pythium spp.

Suppression of Pythium and Phytophthora Damping-Off of Rooibos by Compost and a Combination of Compost and Nonpathogenic Pythium Taxa.

Pathogenic oomycetes, including Phytophthora cinnamomi and several Pythium spp. (Pythium irregulare, P. mamillatum, P.

Pythium cederbergense sp. nov. and related taxa from Pythium clade G associated with the South African indigenous plant Aspalathus linearis (rooibos).

The genus Pythium consists of more than 120 species and is subdivided into 11 phylogenetic clades (A-K) based on internal transcribed spacer (ITS) region sequence data. Pythium clade G contains only seven known species, with most not being well described. Our study characterized 12 Pythium isolates from Aspalathus linearis (rooibos) that fit into clade G.

Recent Genotypes of Phytophthora infestans in the Eastern United States Reveal Clonal Populations and Reappearance of Mefenoxam Sensitivity.

Isolates of Phytophthora infestans (n = 178) were collected in 2002 to 2009 from the eastern United States, Midwestern United States, and eastern Canada. Multilocus genotypes were defined using allozyme genotyping, and DNA fingerprinting with the RG-57 probe. Several previously described and three new mulitilocus genotypes were detected.

Phylogenetic and Biological Characterization of Fusarium oxysporum Isolates Associated with Onion in South Africa.

Fusarium oxysporum f. sp. cepae causes Fusarium basal rot of onion, a disease of worldwide importance.

Molecular analyses of Pythium irregulare isolates from grapevines in South Africa suggest a single variable species.

The Pythium irregulare species complex is the most common and widespread Pythium spp. associated with grapevines in South Africa. This species complex has been subdivided into several morphological and phylogenetic species that are all highly similar at the sequence level [internal transcribed spacer (ITS) and cytochrome c oxidase (cox) regions].

Molecular identification of two vegetative compatibility groups of Fusarium oxysporum f. sp. cepae.

Fusarium oxysporum f. sp. cepae, which causes basal rot of onion, consists of seven vegetative compatibility groups (VCGs 0420 to 0426) and several single-member VCGs (SMVs).

Oogonial biometry and phylogenetic analyses of the Pythium vexans species group from woody agricultural hosts in South Africa reveal distinct groups within this taxon.

Pythium vexans fits into the internal transcribed spacer (ITS) clade K sensu Lévesque & De Cock (2004). Within clade K, P. vexans forms a distinct clade containing two enigmatic species, Pythium indigoferae and Pythium cucurbitacearum of which no ex-type strains are available.

Penicillium Species Associated with Preharvest Wet Core Rot in South Africa and Their Pathogenicity on Apple.

Symptoms associated with the core region of apple fruits (Malus domestica) can be classified as moldy core (MC), wet core rot (WCR), and dry core rot (DCR). Infections leading to WCR are thought to occur primarily postharvest, although in South Africa preharvest symptoms also have been reported. The first aim of this study was to investigate the causative agent(s) of preharvest WCR by isolating fungi from eight internal positions in asymptomatic, MC, WCR, and DCR fruits.

Morphological and phylogenetic analyses of Pythium species in South Africa.

The genus Pythium is important in agriculture, since it contains many plant pathogenic species, as well as species that can promote plant growth and some that have biocontrol potential. In South Africa, very little is known about the diversity of Pythium species within agricultural soil, irrigation and hydroponic systems. Therefore, the aim of the study was to characterise a selection of 85 Pythium isolates collected in South Africa from 1991 through to 2007.

Pythium recalcitrans sp. nov. revealed by multigene phylogenetic analysis.

A new species of Pythium collected from grapevine roots (Vitis vinifera) in South Africa and roots of common beet (Beta vulgaris) in Majorca, Spain, is described. The phylogenetic position of the new species was investigated by multigene sequence analyses of the internal transcribed spacers (ITS1 and ITS2) of the rDNA region, as well as three other nuclear and three mitochondrial coding genes. Maximum likelihood phylogenetic analyses based on ITS rDNA and concatenated beta-tubulin and cytrochrome c oxidase II alignment place Pythium recalcitrans together with P.

Intraspecific and within-isolate sequence variation in the ITS rRNA gene region of Pythium mercuriale sp. nov. (Pythiaceae).

Sixteen Pythium isolates from diverse hosts and locations, which showed similarities in their morphology and sequences of the internal transcribed spacer (ITS) region of their rRNA gene, were investigated. As opposed to the generally accepted view, within single isolates ITS sequence variations were consistently found mostly as part of a tract of identical bases (A-T) within ITS1, and of GT or GTTT repeats within the ITS2 sequence. Thirty-one different ITS sequences obtained from 39 cloned ITS products from the 16 isolates showed high sequence and length polymorphisms within and between isolates.

Toward improvements of oomycete transformation protocols.

Some of the most important plant pathogens worldwide are oomycetes, and billions of dollars are expended annually to suppress diseases they cause. More efficient disease suppression technologies will be derived from a better understanding of the basic biology of these organisms, but inefficient transformation currently limits basic molecular investigations. Of the various approaches, transformation of protoplasts using polyethylene glycol/calcium chloride remains most successful, but the frequency of stable transformation remains low and inconsistent.

Population genetic structure of Plasmopara viticola in the Western Cape Province of South Africa.

SUMMARY Plasmopara viticola populations in South Africa were studied for two consecutive grape growing seasons, in an organically managed and a conventional fungicide-sprayed vineyard. Three to four samplings in each season were genotyped with four microsatellite markers (GOB, CES, ISA and BER). Population differentiation (Fst) between the conventional fungicide-sprayed vineyard and organically managed vineyard was low (0.

Core promoter structure in the oomycete Phytophthora infestans.

We have investigated the core promoter structure of the oomycete Phytophthora infestans. The transcriptional start sites (TSS) of three previously characterized P. infestans genes, Piexo1, Piexo3, and Piendo1, were determined by primer extension analyses.

Characterization of 1,3-beta-glucanase and 1,3;1,4-beta-glucanase genes from Phytophthora infestans.

Three putative exo-1,3-beta-glucanase genes (Piexo1, Piexo2, Piexo3), one endo-1,3-beta-glucanase (Piendo1) and one endo-1,3;1,4-beta-glucanase (Piendo2) gene were cloned and characterized from the oomycete Phytophthora infestans. Southern hybridization revealed that Piexo1, Piexo2, Piexo3, and Piendo2 are single copy, and that Piendo1 is encoded by two copies. Furthermore, the analyses showed that for each gene, one or two closely related gene family members were present.